The present invention relates generally to spacecraft control methods, and more particularly, to methods that provide stationkeeping maneuvering of spacecraft using reflected solar radiation pressure via yaw biasing and mechanical means.
There has been unusual orbital behavior observed in Globalstar spacecraft deployed by the assignee of the present invention, and in particular, spacecraft that are currently configured to operate with a yaw bias while in yaw steering mode. These spacecraft, all located in plane `A` of the Globalstar constellation, have been observed to gain or lose orbit energy in the form of changes to the absolute semi-major axis. This energy source/sink exceeds the atmospheric drag force by up to an order of magnitude. This energy exchange is observable, repeatable, and has been found to be a directly proportional function of the orbit plane `beta` angle. Careful analysis has shown the source of the force to be a solar radiation pressure differential due to reflected solar energy resulting from operations with yaw biases. The resulting orbital behavior has implications for both the stationkeeping strategy of the current Globalstar spacecraft as well as design implications for future spacecraft that will operate with yaw steering. With these considerations in mind, future yaw steered spacecraft operating in the low earth orbit (LEO) regime may take advantage of differential solar radiation reflection to augment thrusters for orbit maintenance.
More specifically, in observing the orbital behavior of Globalstar spacecraft operating in yaw steering mode with a 165 degree yaw bias, it has been discovered that solar radiation pressure (SRP) can apply a force parallel or antiparallel to the orbital velocity vector. This force has an average sign around the entire orbit which is the same as the sign of the orbit plane beta angle. When the bias is between 90 and 180 degrees or 0 and -90 degrees, and the orbit plane beta angle is positive, the force is posigrade, and when the orbit plane beta angle is negative, the force is retrograde. When the bias is between 0 and 90 degrees or between -90 and -180 degrees, this is reversed. The sign of the average force is given by -sign(bias) * sign(beta angle). It would be desirable to use this force to advantage to control stationkeeping activity of the spacecraft.
Accordingly, it is an objective of the present invention to provide for methods that provide stationkeeping maneuvering of spacecraft using reflected solar radiation pressure via yaw biasing and mechanical means.